Apparatus and method for reducing instances of pump de-priming

ABSTRACT

Abruptly shutting down an electrolyzer cell module during normal operation may, in some instances, be necessary when one or more process and operating parameters uncontrollably deviate into an unsafe range. However, abruptly shutting down an electrolyzer cell module may have residual effects that make it difficult to restart the electrolyzer cell module. In particular, in some instances a circulation pump is de-primed by the accumulation of gas bubbles within the circulation pump, which normally do not exist during normal operation since a fluid containing dissolved gas molecules is pressurized to ensure that the gas remains dissolved. In some embodiments of the invention there is provided a modified safety system that can controllably shutdown an electrolyzer cell module in an emergency situation so as to prevent instances of pump de-priming.

PRIORITY CLAIM

This application claims the benefit, under 35 USC 119(e), of U.S.Provisional Application No. 60/504,218 that was filed on Sep. 22, 2003,and the entire contents of which is hereby incorporated by reference.

FIELD OF THE INVENTION

The invention relates to electrolyzer cells and, in particular to anapparatus and method suited for controlling an electrolyzer cell module.

BACKGROUND OF THE INVENTION

An electrolyzer cell is a type of electrochemical device that usesenergy to dissociate a compound liquid into its components. For example,water can be dissociated into hydrogen and oxygen (e.g. H₂O→H₂+O₂).

In practice, a number of electrolyzer cells are arranged into a stack toproduce sizable amounts of one or more of the components of a compoundliquid. To this end, the electrolyzer cell stack is included in a modulethat includes a suitable combination of supporting elements,collectively termed a balance-of-plant system, which is specificallyconfigured to maintain operating parameters related to the operation ofthe stack.

Typically, during the normal operation of an electrolyzer cell module,process gases and fluids are pressurized. For example, the water withinthe electrolyzer cell module is pressurized so that oxygen produced inthe stack remains dissolved within the water, since large gas bubbleswill reduce efficiency. In some emergency situations, the operation ofan electrolyzer cell module is abruptly halted and power provided to thebalance-of-plant elements is cut-off. As a result, the pressure in thevarious gas/fluid lines is released, which causes the formation ofrelatively large gas bubbles that sometimes make it difficult to restartthe electrolyzer cell module.

SUMMARY OF THE INVENTION

According to aspects of an embodiment of the invention there is providedan electrolyzer cell module having: an electrolyzer cell stack forelectrolysing a compound liquid to produce at least one gas; a pluralityof balance-of-plant elements connected to the electrolyzer cell stack,for regulating the operation of the electrolyzer cell stack; a safetysystem connected to at least some of the balance-of-plant elements andthe electrolyzer cell stack, for monitoring at least one process andoperating parameter related to the operation of the electrolyzer cellmodule and evaluating whether or not at least one alarm threshold hasbeen violated by the at least one process and operating parameter; acomputer usable medium, in communication with the safety system, havingcomputer program readable code means embodied therein for emergencystoppage of the normal operation of the electrolyzer cell module whenthe at least one alarm threshold has been violated, the computer programreadable code means including: instructions for stopping theelectrolysis of the compound liquid within the electrolyzer cell stack,thereby stopping the production of the at least one gas; instructionsfor operating the electrolyzer cell module so as to flush out residualamounts of the at least one gas dissolved in the compound liquid over atime period; and, instructions for cutting-off power, at the end of thetime period, to all of the elements included in the electrolyzer cellmodule required for flushing out residual amounts of the at least onegas dissolved in the compound liquid, to shut-down the electrolyzer cellstack.

In some embodiments the computer program readable code means alsoincludes: instructions for cutting-off power to some of thebalance-of-plant elements included in the electrolyzer cell module,while continuing to provide power to other balance-of-plant elementsrequired to flush out the residual amounts of the at least on gasdissolved in the compound liquid within the electrolyzer cell module. Insome related embodiments the balance-of-plant elements that continue toreceive power during an emergency stoppage include a circulation pumpand pressure regulating devices.

In some embodiments the electrolyzer cell module also includes apressure release means that is operable to slowly and controllablyrelease the pressure within the electrolyzer cell module as it is beingturned off. In some specific instances the pressure release means incomprised of a combination of valves that includes, without limitation,a need/orifice valve and a second valve connected in series, wherein thesecond valve is opened when the electrolyzer cell module is shut down.

According to other aspects of an embodiment of the invention there isprovided an emergency stoppage method of operating an electrolyzer cellmodule that includes a number of balance-of-plant elements and anelectrolyzer cell stack, the method including: stopping electrolysis ofa compound liquid, thereby stopping the production of at least one gasdissolved in the compound liquid; flushing out residual amounts of theat least one gas evolved from the compound liquid by operating some ofthe balance-of-plant elements included in the electrolyzer cell moduleand not others; and, cutting-off power, to all of the elements includedin the electrolyzer cell module required for flushing out the residualamounts of the at least one gas dissolved in the compound liquid, toshut-down the operation of the electrolyzer cell stack.

In some embodiments the method also includes a step of controllablyreleasing the pressure within the electrolyzer cell module as theresidual amounts of the at least one gas are flushed from theelectrolyzer cell module. In some specific instance the method alsoincludes the step of cutting-off power to some of the balance-of-plantelements included in the electrolyzer cell module, while continuing toprovide power to other balance-of-plant elements required to flush outthe residual amounts of the at least on gas dissolved in the compoundliquid within the electrolyzer cell module.

Other aspects and features of the present invention will becomeapparent, to those ordinarily skilled in the art, upon review of thefollowing description of the specific embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show moreclearly how it may be carried into effect, reference will now be made,by way of example, to the accompanying drawings that illustrate aspectsof embodiments of the present invention and in which:

FIG. 1 is a simplified schematic drawing of an electrolyzer cell;

FIG. 2 is a first detailed schematic drawing of an electrolyzer cellmodule according to aspects of an embodiment of the invention;

FIG. 3 is a second detailed schematic drawing of an electrolyzer cellmodule according to aspects of an alternative embodiment of theinvention;

FIG. 4 is a flow chart illustrating a high-level method of operating anelectrolyzer cell module according to aspects of an embodiment of theinvention; and

FIG. 5 is a flow chart depicting the general steps provided in anemergency stop program according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Abruptly shutting down an electrolyzer cell module during normaloperation may, in some instances, be necessary when one or more processand operating parameters uncontrollably deviate into an unsafe range.However, abruptly shutting down an electrolyzer cell module may haveresidual effects that make it difficult to restart the electrolyzer cellmodule. In particular, in some instances a circulation pump is de-primedby the accumulation of gas bubbles within the circulation pump, whichnormally do not exist during normal operation since a fluid containingdissolved gas molecules is pressurized to ensure that the gas remainsdissolved. In some embodiments of the invention there is provided amodified safety system that can controllably shut down an electrolyzercell module in an emergency situation so as to prevent instances of pumpde-priming.

There are a number of different electrochemical cell technologies and,in general, this invention is expected to be applicable to all types ofelectrochemical cells. Very specific example embodiments of theinvention have been developed for use with Proton Exchange Membrane(PEM) electrolyzer cells. Various other types of electrolyzer cells alsoinclude, without limitation, Solid Polymer Water Electrolyzers (SPWE).Similarly, various types of fuel cells include, without limitation,Alkaline Fuel Cells (AFC), Direct Methanol Fuel Cells (DMFC), MoltenCarbonate Fuel Cells (MCFC), Phosphoric Acid Fuel Cells (PAFC), SolidOxide Fuel Cells (SOFC) and Regenerative Fuel Cells (RFC).

Referring to FIG. 1, shown is a simplified schematic diagram of a ProtonExchange Membrane (PEM) electrolyzer cell, simply referred to aselectrolyzer cell 100 hereinafter, that is described herein toillustrate some general considerations relating to the operation ofelectrochemical cells. It is to be understood that the present inventionis applicable to various configurations of electrochemical cell modulesthat each include one or more electrochemical cells.

The electrolyzer cell 100 includes an anode electrode 210 and a cathodeelectrode 410. The anode electrode 210 includes a water input port 220and a water/oxygen output port 240. Similarly, the cathode electrode 410includes a water input port 420 and a water/hydrogen output port 440. Anelectrolyte membrane 300 is arranged between the anode electrode 210 andthe cathode electrode 410.

The electrolyzer cell 100 also includes a first catalyst layer 230arranged between the anode electrode 210 and the electrolyte membrane300, and a second catalyst layer 430 arranged between the cathodeelectrode 410 and the electrolyte membrane 300.

In order to energize the electrolyzer cell 100, a voltage source 117 iscoupled between the anode and cathode electrodes 210, 410.

In operation, water is introduced into the anode electrode 210 via thewater input port 220. The water is dissociated electrochemicallyaccording to reaction (1), given below, in the presence of theelectrolyte membrane 300 and the first catalyst layer 230.H₂O→2H⁺+2e ⁻1/2O₂  (1)The chemical products of reaction (1) are hydrogen ions (i.e. cations),electrons and oxygen. The hydrogen ions pass through the electrolytemembrane 300 to the cathode electrode 410 while the electrons are drawnthrough the voltage source 117. Water containing dissolved oxygenmolecules is drawn out through the water/oxygen output port 240. Thewater is pressurized to ensure that the oxygen molecules remaindissolved in the water and do not form relatively large gas bubbles.

Simultaneously, additional water is introduced into the cathodeelectrode 410 via the water input port 420 in order to provide moistureto the cathode side of the electrolyte membrane 300.

The hydrogen ions (i.e. protons) are electrochemically reduced tohydrogen molecules according to reaction (2), given below, in thepresence of the electrolyte membrane 300 and the second catalyst layer430. That is, the electrons and the ionized hydrogen atoms, produced byreaction (1) in the anode electrode 210, are electrochemically consumedin reaction (2) in the cathode electrode 410.2H₂ ⁺+2e ³¹ →H₂  (2)

The water containing dissolved hydrogen molecules is drawn out throughthe water/hydrogen output port 440. The electrochemical reactions (1)and (2) are complementary to one another and show that for each oxygenmolecule (O₂) that is electrochemically produced two hydrogen molecules(H₂) are electrochemically produced.

Although only one electrolyzer cell is illustrated in FIG. 1, it iscommonly understood that in practice a number of electrochemical cells,all of one type, can be arranged in stacks having common elements, suchas process gas/fluid feeds, drainage, electrical connections andregulation devices. That is, an electrochemical cell module is typicallymade up of a number of singular electrochemical cells connected inseries to form an electrochemical cell stack. The electrochemical cellmodule also includes a suitable combination of structural elements,mechanical systems, hardware, firmware and software that is employed tosupport the function and operation of the electrochemical cell stack.Such items include, without limitation, piping, sensors, regulators,current collectors, seals, insulators, actuators, switches andelectromechanical controllers.

Referring now to FIG. 2, illustrated is a simplified schematic diagramillustrating an electrolyzer cell module 10 a that is configured todissociate water (H₂O) into hydrogen (H₂) and oxygen (O₂). Theelectrolyzer cell module 10 a includes an electrolyzer cell stack 11, apower supply 117, a hydrogen collection device 39, an oxygen collectiondevice 20, a water supply tank 16 and a suitable combination ofbalance-of-plant elements.

Those skilled in the art will appreciate that shown in FIG. 2 are onlythose balance-of-plant elements necessary to describe aspects of thisexample embodiment of the invention. Generally, balance-of-plantelements can be roughly divided into two groups. A first group may bedefined as a suitable combination of supporting apparatus andelectromechanical systems that includes, without limitation, elementssuch as heaters, filters, pumps, humidifiers, valves and the like. Asecond group may be defined as a suitable combination of control andsensor systems that includes, without limitation, sensors, switches,valves, hardware, software, firmware and the like.

In some embodiments, the control and sensor systems include acentralized control system including for example a microcontrollerand/or a computer program readable code means for monitoring andregulating the operation of an electrolyzer cell module, includingportions of the supporting apparatus and electromechanical systems. Inalternative embodiments, distributed control systems/controllers areprovided along with or in place of a centralized control system.Generally, the sensors and the switches are electronically coupled tothe aforementioned centralized and/or distributed control systems, whichprocess sensor readings and signal the switches and otherelectromechanical devices accordingly in order to regulate and in somecases shut down an electrolyzer cell module.

With specific reference to FIG. 2, the electrolyzer cell module 10 aincludes a controller 90 that is used to manage the operations of theelectrolyzer cell module 10 a. Although the controller 90 is not shownspecifically connected to any of the other elements included in theelectrolyzer cell module 10 a of FIG. 2, those skilled in the art willgenerally appreciate that a controller can be connected to any suitablecombination of elements included in an electrolyzer cell module.

The controller 90 includes a modified safety system 93, an emergencystop program 97 and at least one application program 95 used to managethe normal operations of the electrolyzer cell module 10 a. To that end,in the present embodiment of the invention, the controller 90 includes amemory for storing a computer program readable code means havinginstructions for the modified safety system 93, the emergency stopprogram 97 and the at least one application program 95.

The modified safety system 93, in accordance with an embodiment of theinvention, is capable of calling an alarm recovery sequence and/orcalling the emergency stop program 97, in the event that an alarmthreshold has been violated. Details relating to various embodiments ofmodified safety programs are provided in the applicant's co-pending U.S.patent application Ser. No.______[Attorney Ref: 9351-493], which wasfiled on the same day as this application and is hereby incorporated byreference.

The electrolyzer cell stack 11 shown in FIG. 2 includes one or more PEMelectrolyzer cells (not shown). Each PEM electrolyzer cell includes anelectrolyte membrane arranged between an anode electrode and a cathodeelectrode as schematically illustrated in FIG. 1. The electrolyzer cellstack 11 has a cathode outlet port 28, an anode inlet port 202 and ananode outlet port 27. The cathode outlet port 28 is fluidly connected toeach of the respective cathode electrodes included in the electrolyzercell stack 11. Similarly, the anode inlet and outlet ports 202, 27 arefluidly connected to each of the respective anode electrodes included inthe electrolyzer cell stack 11. The electrolyzer cell stack 11 alsoincludes respective electrical connections 12, 13 to the anode andcathode terminals of the electrolyzer cell stack 11.

The power supply 117 is coupled to the electrical connections 12, 13 ofthe electrolyzer cell stack 11 to energize the electrolyzer cell stack11. A stack disconnect device 48 is also coupled between the electricalconnections 12, 13 of the electrolyzer cell stack 11 and the powersupply 117. Additionally, a current 15 and a voltage sensor 14 areappropriately arranged between the stack disconnect device 48 and thepower supply 117 to measure the current drawn by the electrolyzer cellstack 11 and the voltage across the electrical connections 12, 13.

The stack disconnect device 48 is operable between two states. In afirst state, the stack disconnect device 48 electrically couples thepower supply 117 to the electrolyzer cell stack 11. In a second state,the stack disconnect device 48 electrically isolates the power supply117 from the electrolyzer cell stack 11. In some embodiments, switchingthe stack disconnect device 48 between the two states is, for example,controlled by a central and/or local distributed control system, whichmay use readings from the current and voltage sensors 15, 14 in thisprocess.

The hydrogen collection device 39 includes an output port 5; anotheroutput port and an input port. In some embodiments, the output port 5serves as a tap for hydrogen collected by the hydrogen collection device39, and is also connectable to other downstream components (not shown).The input of the hydrogen collection device 39 is coupled to the cathodeoutlet port 28 to accept a combination of water and hydrogen from theelectrolyzer cell stack 11. The other output port is coupled to thewater supply tank 16 to return water separated from hydrogen duringoperation.

The oxygen collection device 20 includes an output port 4; anotheroutput port and two input ports. In some embodiments, the output port 4serves as a tap for oxygen collected by the oxygen collection device 20,and is also connectable to other downstream components (not shown). Theother output port is coupled to provide water to the anode inlet port202, and one of the input ports is coupled to receive a combination ofwater and oxygen from the anode outlet port 27. The other input port iscoupled to receive water from the water supply tank 16. That is,according to this specific example, water is provided to theelectrolyzer cell stack 11 from the water supply tank 16 via the oxygencollection device 20, which also recycles water received back from theelectrolyzer cell stack 11.

Optionally, in other embodiments, the water supply tank 16 is alsocoupled to a cathode inlet port of the electrolyzer cell stack 11 tohydrate the respective cathode sides of the membranes included in theelectrolyzer cell stack 11.

In some embodiments, the hydrogen and oxygen collection devices 39, 20each include a condenser, such as, for example, the apparatus describedin the applicant's issued U.S. Pat. No. 6,619,054, which is herebyincorporated by reference.

In some embodiments, the hydrogen collection device 39 has a volume thatis about twice the volume of the oxygen collection device 20. Thisdifference in size accommodates the relative rates of hydrogen andoxygen evolution that will occur according to reactions (1) and (2)described above.

The anode and cathode outlet ports 27, 28 of the electrolyzer cell stack11 are respectively connected to the oxygen and hydrogen collectiondevices 20, 39 through respective combinations of balance-of-plantelements.

Specifically, in this example embodiment, there is a second pressuresensor 30, a first pressure safety switch 33, a first temperature sensor36 and a first heat exchanger 38 arranged along the fluid pathway fromthe cathode outlet port 28 to the hydrogen collection device 39. Thefirst pressure safety switch 33 is operable to send an alarm signal to acentral and/or distributed control system if the pressure of the streamof hydrogen and water exiting the cathode outlet port 28 reaches apredetermined high value. In some embodiments, the first pressure safetyswitch 33 is configured to override and halt the operation of theelectrolyzer cell module 10 a in the event that the pressure is toohigh, which may imply that there is a severe problem with theelectrolyzer cell module 10 a.

The first temperature sensor 36 is coupled to provide the first heatexchanger 38 with a regulation signal. Using the regulation signal fromthe first temperature sensor 36, the first heat exchanger 38 is operableto cool the stream of hydrogen and water exiting the cathode outlet port28, thereby initiating condensation of the water to separate it from thehydrogen within the hydrogen collection device 39.

Similarly, in this example embodiment, there is a first pressure sensor29, a second temperature sensor 31 and a first temperature safety switch32 arranged along the fluid pathway from the anode outlet port 27 to theoxygen collection device 20. The first temperature safety switch 32 isoperable to send an alarm signal to a centralized and/or distributedcontrol system if the temperature of the stream of oxygen and waterexiting the anode outlet port 27 reaches a predetermined high value. Insome embodiments, the first temperature safety switch 32 is configuredto override and halt the operation of the electrolyzer cell module 10 ain the event that the temperature is too high, which may imply thatthere is a severe problem with the electrolyzer cell module 10 a.

The anode inlet port 202 of the electrolyzer cell stack 11 is connectedto receive water from the oxygen collection device 20 through arespective combination of balance-of-plant elements as well.Specifically, a circulation pump 23, a second heat exchanger 22, aresistivity meter 24, a flow switch 25 and preferably a de-ionizingfilter 26 are arranged along the fluid pathway to the anode inlet port202 from the oxygen collection device 20. The second heat exchanger 22is also coupled to receive a regulation signal from the secondtemperature sensor 31 arranged on the fluid pathway originating from theanode outlet port 27.

The circulation pump 23 is operable to force the flow of water into theelectrolyzer cell stack 11. In some embodiments, the circulation pump isof a high-temperature/high-pressure type, and is constructed withmaterials such as Teflon® or Peek®. Using the regulation signal from thesecond temperature sensor 31, the second heat exchanger 22 is operableto adjust the temperature of the water stream entering the electrolyzercell stack 11. The resistivity meter 24 is operable to measure theresistivity of the water flowing into the electrolyzer cell stack 11.The flow switch 25 is operable to send an alarm signal to a centraland/or local distributed control system if the water level is too low.In some embodiments, the de-ionizing filter 26 incorporates organic andparticulate filtering functions.

As a side note, in different embodiments the first and second heatexchangers 38, 22 are made up of different components. For example, inone embodiment the first and second heat exchangers 38, 22 include fansfor temperature regulation by air-heating/cooling, whereas in otherembodiments the first and second heat exchangers 38, 22 include pumpsand coolant fluids for temperature regulation by liquid-heating/cooling.Those skilled in the art will generally appreciate that a heat exchangercan be embodied in a number of different forms, but in each embodimentthe function of a heat exchanger is to serve as a temperature regulationmeans.

There are also a number of balance-of-plant elements arranged along thefluid pathway from the water supply tank 16 to the oxygen collectiondevice 20. Specifically, the water supply tank 16 is connected to theoxygen collection device 20 through a fill pump 17, an organic filter18, a particulate and a de-ionizing filter 19, a check valve 47 and athree-way valve 21. An output of the three-way valve 21 is also coupledback to the water supply tank 16. The check valve 47 is arranged toprevent back flow of water through the fill pump 17 and filters 18, 19.

A first water level indicator 37 is coupled to the oxygen collectiondevice 20 and to the fill pump 17 and the three-way valve 21. The firstwater level indicator 37 is operable to measure the water level in theoxygen collection device 20 and provide a feedback control signal to thefill pump 17 and the three-way valve 21. For example, when the waterlevel in the oxygen collection device 20 is higher than a pre-set highlevel value, the three-way 21 valve is set to re-circulate water back tothe water supply tank 16; or, when the water level is lower than apre-set low level value, the fill pump 17 is signalled to increase therate of water flow.

Comparatively, the balance-of-plant setup between the hydrogencollection device 39 and the water supply tank 16 is quite simple. Asecond water level indicator 45 is coupled to the hydrogen collectiondevice 39 and a purge valve 46 is connected between the hydrogencollection device 39 and the water supply tank 16. The purge valve 46 isoperated by a control signal received from the second water levelindicator 45 coupled to the hydrogen collection device 39. When thewater level in the hydrogen collection device 39 is higher than apre-set level value, the purge valve 46 opens after receiving thecontrol signal from the second water level indicator 45. Once the purgevalve 46 is opened, water can flow from the hydrogen collection device39 to the water supply tank 16. Alternatively, the purged water can bedumped out of the system or used for other purposes (i.e. as a coolant).

The hydrogen collection device 39 also has a safety valve 44 thatautomatically vents gas from the hydrogen collection device 39 when thepressure inside reaches a pre-set upper threshold. Accordingly, thesafety valve 44 aids in the regulation of the hydrogen pressure, whichin this embodiment, is followed by the oxygen pressure via the operationof the pressure following device 34.

In this particular embodiment, the output port 5 of the hydrogencollection device 39 is coupled to a combination of valves.Specifically, the output port 5 is coupled to a backpressure valve 40that is in parallel with a normally open venting valve 41 that isarranged in series with a needle/orifice valve 42. The outputs of thebackpressure valve 40 and the needle/orifice valve 42 are coupled inparallel into a check valve 43.

The backpressure valve 40 is arranged to regulate the hydrogen pressurewithin the hydrogen collection device 39 during the operation of theelectrolyzer cell module 10 b. The hydrogen is preferably stored in alarge low-pressure (e.g. around 100 psi) tank having water drainage toremove whatever small amount of water that could still be present withthe hydrogen. Alternatively, the hydrogen could be stored inlow-pressure storage devices such as metal hydrides. The hydrogen couldalso be further compressed into higher-pressure storage vessels.

The combination of the normally open valve 41 and the needle/orificevalve 42 cooperate to controllably release the pressure within theelectrolyzer cell module 10 a when it is shut down. The normally openventing valve 41 is preferably closed during start-up and opens when theelectrolyzer cell module 10 b shuts down. The normally open valve 41also functions as an emergency pressure relief path when theelectrolyzer cell module 10 b is suddenly stopped in emergencysituations, which reduces the chances that any of the pumps in theelectrolyzer cell modules 23 will be de-primed by the sudden formationof gas bubbles in the system. The needle/orifice valve 42 is arrangedafter the normally open valve 41 to slowly lower the hydrogen pressureto the ambient pressure, after the electrolyzer cell module 10 b is shutdown, again, in order not to de-prime any of the circulation pumps.

The check valve 43 is arranged to prevent back flow into the hydrogencollection device 39 and isolate the hydrogen pressure from pressuresdownstream.

A hydrogen gas sensor 35 is arranged on the output port 4 of the oxygencollection device 20 to detect irregularly high levels of hydrogen inthe oxygen stream, which may indicate that there is a leak somewhere inthe system. The oxygen collection device 20 also has a safety valve 49arranged to vent oxygen should the pressure inside reach a pre-set highvalue.

With continued reference to FIG. 3, the pressure following device 34 isarranged between the output port 4 of the oxygen collection device 20and the hydrogen collection device 39. Specifically, the pressurefollowing device 34 includes a pressure sensor connected to measure thehydrogen pressure in the hydrogen collection device 39, and adome-loaded pressure valve, which is configured as a negative biaspressure regulator, that is connected to the output port 4 of the oxygencollection device 20. The pressure following device 34 measures/sensesthe hydrogen pressure and sets the oxygen pressure via control of thedome-loaded pressure valve. Aspects of pressure following arrangementsaccording to aspects of embodiments of the invention are described ingreater detail in the applicant's co-pending U.S. patent applicationSer. No.______ [Attorney Ref. No: 9351-460], which was filed on the sameday as this application and is hereby incorporated by reference.

During an emergency shutdown process it is preferable that the pressurefollowing device 34 continues operation so as to permit the circulationpumps to flush out gases dissolved in the water so that they do notaccumulate in relatively large bubbles within the electrolyzer cellmodule 10 a. This is desirable since the accumulation of relativelylarge gas bubbles within the electrolyzer cell module 10 a may lead to ade-priming of the circulation pumps.

In this particular embodiment, the hydrogen side of the electrolyzercell stack 11 does not include a pump, and, accordingly the hydrogenpressure is primarily established using the backpressure valve 40. It isbeneficial to the overall system efficiency to keep the hydrogenpressure relatively high in order to reduce the size of hydrogen gasbubbles, which will in turn increase the active reaction area and reducethe amount of current fed to the electrolyzer cell stack 11. Havingsmaller hydrogen bubbles improves efficiency and counteracts anydecrease in efficiency caused by the relatively high pressure(s) of thesystem.

The operation of the electrolyzer cell stack 11 (in FIG. 2) is similarto that of the electrolyzer cell module 100 (in FIG. 1). To brieflyreiterate, the power supply 117 supplies the requisite energy forreactions (1) and (2). Oxygen is produced in the anode electrodesaccording to reaction (1) and then a combination of water and oxygenflows out of the anode outlet port 27 into the oxygen collection device20 where the oxygen is separated from the water. Hydrogen is produced inthe cathode electrodes according to reaction (2) and then a combinationof water and hydrogen flows out of the cathode outlet port 28 into thehydrogen collection device 39 where the hydrogen is separated from thewater.

Referring now to FIG. 3, shown is an electrolyzer cell module 10 b,which includes an alternative pressure following arrangement to thatincluded in the electrolyzer cell module 10 a shown in FIG. 2.Specifically, the electrolyzer cell module 10 b is configured so thatthe hydrogen pressure follows the oxygen pressure, but remains higher.To this end, a pressure following device 34′ is arranged between theoutput port 5 of the hydrogen collection device 39 and the oxygencollection device 20. The pressure following device 34′ includes apressure sensor connected to measure the oxygen pressure in the oxygencollection device 20, and a dome-loaded pressure valve, which isconfigured as a positive bias pressure regulator, that is connected tothe output port 5 of the hydrogen collection device 39. As describedabove, the pressure following device 34′ measures/senses the oxygenpressure and sets the hydrogen pressure via control of the dome-loadedpressure valve. Again, aspects of pressure following arrangementsaccording to aspects of embodiments of the invention are described ingreater detail in the applicant's co-pending U.S. patent applicationSer. No.______[Attorney Ref. No: 9351-460], which was incorporated byreference above.

During an emergency shutdown process it is preferable that the pressurefollowing device 34′ continues operation so as to permit the circulationpumps to flush out gases dissolved in the water so that they do notaccumulate in relatively large bubbles within the electrolyzer cellmodule 10 b. This is desirable since the accumulation of relativelylarge gas bubbles within the electrolyzer cell module 10 b may lead to ade-priming of the circulation pumps.

Moreover, the output port 5 of the hydrogen collection device 39 is nowonly connected to the normally open venting valve 41 that is arranged inseries with the check valve 43. The normally open venting valve 41 andthe check valve 43 operate as described above. Additionally, the outputport 4 of the oxygen collection device 20 is connected to aneedle/orifice valve 42′ that is further connected in series to anothernormally open valve 41′. The needle/orifice valve 42′ and the normallyopen valve 41′ operate to regulate the oxygen pressure during theoperation of the electrolyzer cell module 10 c.

The combination of the normally open valve 41′ and the needle/orificevalve 42′ cooperate to controllably release the pressure within theelectrolyzer cell module 10 b when it is shut down, in a similar mannerto the combination of the normally open valve 41 and the needle/orificevalve 42 descrfibed above. The normally open venting valve 41 ispreferably closed during start-up and opens when the electrolyzer cellmodule 10 b shuts down. The normally open valve 41 also functions as anemergency pressure relief path when the electrolyzer cell module 10 b issuddenly stopped in emergency situations, which reduces the chances thatany of the pumps in the electrolyzer cell modules 23 will be de-primedby the sudden formation of gas bubbles in the system. The needle/orificevalve 42 is arranged after the normally open valve 41 to slowly lowerthe hydrogen pressure to the ambient pressure, after the electrolyzercell module 10 b is shut down, again, in order not to de-prime any ofthe circulation pumps.

FIG. 4 is a flow chart illustrating a high-level method of operating anelectrolyzer cell module according to aspects of an embodiment of theinvention. At step 4-0, the electrolyzer cell module is energized and aninitialization sequence, including basic checks, occurs at step 4-1. Thebasic checks include, without limitation, checks for control systemreadiness, the presence of electric power and pneumatic air pressure.

After the basic system checks are complete, the electrolyzer cell moduleenters a standby mode in step 4-2. During the standby mode, the controlsystem waits for a start-up command from an operator or anotherautomated machine.

Once a start-up command has been received, a start-up sequence iscommenced at step 4-3. During the start-up sequence the electrolyzercell module is readied for normal operation. Examples of operations thatoccur during a start-up sequence include, without limitation, a waterfill process, priming of pumps, water polishing, pressurization, andhydrogen purging.

After the start-up sequence 4-3, a run mode is started at step 4-4. Therun mode can end in at least three different ways, which include,without limitation, normal shutdown initiated by an operator or anotherautomated machine, through an alarm recovery sequence at steps 4-5 and4-6, and by an emergency stoppage at step 4-7. The alarm recoverysequences and emergency stoppages result from safety system logic thatis included in the control system for an electrolyzer cell module.Examples describing how the safety system logic can be incorporated intothe control system for an electrolyzer cell module are described in theapplicant's copending U.S. patent application Ser. No.______[AttorneyRef: 9351-493], which was incorporated by reference above. It is worthnoting here that an alarm recovery sequence is only followed by anemergency stoppage if the alarm recovery sequence is not effectivecorrecting the conditions that called for the alarm recovery sequence inthe first place.

In some embodiments a control system is provided with a computer programreadable code means that has instructions that mirror the method stepsdescribed below. Moreover, those skilled in the art will appreciate thatthese methods may be modified without departing from the scope of theinventive aspects specifically described herein.

Referring now to FIG. 5, illustrated is a flow chart depicting thegeneral steps provided in an emergency stop program according to oneembodiment of the invention. Once a safety system concludes that anemergency stoppage is the only way left to deal with violated alarmconditions within an electrolyzer cell module the emergency stop programis started at step 5-1.

With further reference to FIGS. 2 and 3, at step 5-2 the electrolyzercell stack 11 is disconnected from the power supply 117. Then at step5-3, power supplied to the balance-of-plant elements not related to thecirculation pump 23 and the pressure following devices 34 and 34′ iscut-off. That is, the circulation pump 23 and the pressure regulation ofthe line is maintained until gases dissolved in the water within theelectrolyzer cell module (10 a or 10 b) can be flushed from the system,leaving the behind relatively pure water. This process will take somefinite amount of time, depending upon the exact configuration of anelectrolyzer cell module. Simultaneously, pressure is slowly released byway of the normally open valve 41 and the needle/orifice valve 42 (inFIG. 2) or the normally open valve 41′ and the needle/orifice valve 42′.Normally open valves require power to close the valve, but are normallyopen when no power is supplied. Accordingly, during an emergencystoppage power does not need to be supplied to the normally open valve41 or 41′. However, if the normally open valves were replaced withnormally closed valves, power would be required for these valves toremain open during an emergency stoppage.

At step 5-4 it is determined whether or not an emergency timer hasexpired. The emergency timer provides a count down period that has aduration that is about as long as the finite amount of time it takes toflush out the gases from the electrolyzer cell module. If the emergencytimer has not expired (no path, step 54), then the balance-of-plantelements, such as the circulation pump 23, required to flush theresidual gas from the electrolyzer cell module continue to be powered atstep 5-5 while the emergency timer is checked again at step 5-4, after ashort delay. On the other hand, if the emergency timer has expired (yespath, step 54), then it is assumed that the most of the residual gasleft in the electrolyzer cell module has been expelled and the entireelectrolyzer cell module is shut down, including elements such as thecirculation pump 23 and the pressure following devices 34 and 34′.

While the above description provides examples according to aspects ofembodiments of the invention, it will be appreciated that the presentinvention is susceptible to modification and change without departingfrom the fair meaning and scope of the accompanying claims. Accordingly,what has been described is merely illustrative of the application ofsome aspects of embodiments of the invention. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described herein.

1. An electrolyzer cell module comprising: an electrolyzer cell stackfor electrolysing a compound liquid to produce at least one gas; aplurality of balance-of-plant elements connected to the electrolyzercell stack, for regulating the operation of the electrolyzer cell stack;a safety system connected to at least some of the balance-of-plantelements and the electrolyzer cell stack, for monitoring at least oneprocess and operating parameter related to the operation of theelectrolyzer cell module and evaluating whether or not at least onealarm threshold has been violated by the at least one process andoperating parameter; a computer usable medium, in communication with thesafety system, having computer program readable code means embodiedtherein for emergency stoppage of the normal operation of theelectrolyzer cell module when the at least one alarm threshold has beenviolated, the computer program readable code means including:instructions for stopping the electrolysis of the compound liquid withinthe electrolyzer cell stack, thereby stopping the production of the atleast one gas; instructions for operating the electrolyzer cell moduleso as to flush out residual amounts of the at least one gas dissolved inthe compound liquid over a time period; and instructions for cutting-offpower, at the end of the time period, to all of the elements included inthe electrolyzer cell module required for flushing out residual amountsof the at least one gas dissolved in the compound liquid, to shut-downthe electrolyzer cell stack.
 2. An electrolyzer cell module according toclaim 1, wherein the computer program readable code means furthercomprises: instructions for cutting-off power to some of thebalance-of-plant elements included in the electrolyzer cell module,while continuing to provide power to other balance-of-plant elementsrequired to flush out the residual amounts of the at least on gasdissolved in the compound liquid within the electrolyzer cell module. 3.An electrolyzer cell module according to claim 2, wherein thebalance-of-plant elements that continue to receive power during anemergency stoppage include a circulation pump and pressure regulatingdevices.
 4. An electrolyzer cell module according to claim 1 furthercomprising a pressure release means that is operable to slowly andcontrollably release the pressure within the electrolyzer cell module asit is being turned off.
 5. An electrolyzer cell module according toclaim 4, wherein the pressure release means in comprised of acombination of valves.
 6. An electrolyzer cell module according to claim5, wherein the combination of valves is comprised of a need/orificevalve and a second valve connected in series, wherein the second valveis opened when the electrolyzer cell module is shut down.
 7. Anelectrolyzerr cell module according to claim 6, wherein the second valveis one of a normally open valve and a normally closed valve.
 8. Anelectrolyzer cell module according to claim 4 further comprising ahydrogen collection device and an oxygen collection device.
 9. Anelectrolyzer cell module according to claim 8, wherein the pressurerelease means is connected to one of the hydrogen collection device andthe oxygen collection device.
 10. An emergency stoppage method ofoperating an electrolyzer cell module that includes a number ofbalance-of-plant elements and an electrolyzer cell stack, the methodcomprising: stopping electrolysis of a compound liquid, thereby stoppingthe production of at least one gas dissolved in the compound liquid;flushing out residual amounts of the at least one gas evolved from thecompound liquid by operating some of the balance-of-plant elementsincluded in the electrolyzer cell module and not others; and cutting-offpower, to all of the elements included in the electrolyzer cell modulerequired to flush out the residual amounts of the at least one gasdissolved in the compound liquid, to shut-down the operation of theelectrolyzer cell stack.
 11. A method according to claim 10 furthercomprising: controllably releasing the pressure within the electrolyzercell module as the residual amounts of the at least one gas are flushedfrom the electrolyzer cell module.
 12. A method according to claim 11further comprising: cutting-off power to some of the balance-of-plantelements included in the electrolyzer cell module, while continuing toprovide power to other balance-of-plant elements required to flush outthe residual amounts of the at least on gas dissolved in the compoundliquid within the electrolyzer cell module.